For the past three years we have conducted a blood pressure screening program in a selected number of Metropolitan St. Louis high schools which helped establish normal blood pressure standards for the ages 14-18 years based upon a sample of approximately 15,000 subjects. About 5% were found to be hypertensive (1.65 S.D. above the mean) with no apparent cause as shown after a comprehensive in-hospital evaluation. Two of those schools will be the source of hypertensive subjects who will be studied: (1) To determine whether endurance exercise training is effective, by itself, as a therapeutic measure for lowering blood pressure to normal. (2) To determine whether exercise-training is effective in maintaining blood pressure in the normal range over a period of a year. (3) To obtain information regarding the effects of exercise-training on heart rate, cardiac output, myocardial contractile function, and peripheral vascular resistance in hypertensive adolescents. (4) To obtain information regarding the effects of exercise-training on plasma catecholamines.